This invention relates to a cartridge containing a substance for the preparation of a beverage adapted to extraction machines operating by fluid under pressure.
There are several reasons for the use of cartridges for the preparation of a beverage, above all in the field of espresso-type coffees extracted under pressure, namely, hygiene, optimal keeping of the coffee, ease of use, better control of the quality of the coffee obtained and good reproducibility of the extraction conditions. Among the variety of cartridges available, only closed cartridges which open under the pressure of the injected water satisfy the requirements mentioned above. These cartridges are distinguished by their opening system. In addition, they are substantially impermeable to moisture and preferably to oxygen.
The all-aluminium cartridge according to Swiss Patent No. 605 293 has a base face which is larger in diameter than its upper face, and because it is in the form of an inverted frustum, it is not compatible with conventional espresso-type coffee machines and accordingly requires a specifically designed extraction machine. In addition, the base face has a membrane which contains a line of weakening for tearing preferentially under the effect of pressure, but that has a disadvantage of increasing the complexity and price of the cartridge, because the materials used have to be treated with considerable precision if opening of the cartridge is to be correct and reproducible. Further, the cartridge has a thick filter to retain the coffee grounds.
Another cartridge has been designed to be used in a process in which, in a first step, artificially weakened zones are formed in the lower membrane by mechanical action and, in a second step, the capsule is opened by tearing of the artificially weakened zones under the pressure of the injected water. One such process, which is described in French Patents Nos. 1 536 031 and 2 033 190, has numerous disadvantages.
Swiss patent application No. 458 099 relates to an installation for the preparation of a beverage in which a cartridge is extracted under pressure. The cartridge, which may contain ground coffee, consists of two stiff foils of plastic or aluminium, which are perforated and welded to one another, surrounding a porous envelope, containing the substance to be extracted of which the lower face is covered with a thin film of thermoplastic material which melts in the presence of the hot extraction liquid.